The use of an optical fiber bus to interconnect electronic subsystems such as computers in a multi-processor system or switching units in a communication system offers high data rate transmission and eliminates the electrical coupling noise problems of electrical transmission subsystems. In order to achieve the high data rate, it is necessary to rapidly turn on and off the lasers or LEDs that are driving the optical fiber bus. A laser can be turned on from a sub-threshold bias or biased state at extremely high speeds but have a relatively slow turn-on time from an off state. The sub-threshold bias state is an intermediate state between the on and off states in which a laser only emits a small amount of light. Similarly, a laser can be switched to a sub-threshold bias state much more rapidly than it can be returned to a totally off state. Because of this characteristic, lasers are operated by leaving them in the biased state and by pulsing them to the on state and back to biased state to communicate data. This technique works extremely well where only one laser is driving an optical fiber.
A problem arises in a system where a number of lasers are driving a optical fiber bus since in the biased state each laser emits a small amount of light. The light output from the lasers in the biased state is summed on the bus and many reach an intensity where one laser's output in the on state cannot be detected because it is masked by the summed outputs of the lasers in the biased state. Similarly, in order for LEDs to turn on rapidly, they also must be biased to a point where they are emitting light.